


fasten up

by momo314



Category: Pocket Monsters: Sword & Shield | Pokemon Sword & Shield Versions
Genre: Established Relationship, F/M, Light Dysphoria, Plot What Plot/Porn Without Plot, Post-Canon, Sibling Incest, Strap-Ons, Trans Male Character, Underage Sex
Language: English
Status: Completed
Published: 2020-02-02
Updated: 2020-02-02
Packaged: 2021-02-27 19:21:17
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 3,379
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22530877
Author URL: https://archiveofourown.org/users/momo314/pseuds/momo314
Summary: Marnie buys her brother a strap-on. They have a pretty good time trying it out.
Relationships: Nezu | Piers/Mary | Marnie
Comments: 6
Kudos: 48





	fasten up

**Author's Note:**

> Takes place (shortly) after the post-game. I tend to go with 14 and 22~ for ages, but there's no concrete mentions if you want to imagine them differently.

"Big bro," came Marnie's voice, light, testing the waters. They were splayed together in her bed, still wet with sweat and comfortably nestled against each other. "Mind if I show ya somethin'?"

"Go for it." Piers unhooked his arms around her waist so she could crawl away in order to retrieve—whatever it was that she wanted to show him. Though right now she was showing him a great view of her arse as she hung off the edge of the bed and peered underneath. Even if Piers had given Marnie a trembling orgasm mere minutes ago, he still wanted to grab her by the waist and put his mouth to her cunt all over again.

The momentary thought was lost when Marnie scooted back toward him, holding a shopping bag. "I dunno if you'll like it, but I thought you could use it..."

Piers barely registered the bag's logo as belonging to a local sex shop before Marnie opened it. "Sis!" His eyes felt like they might pop out of his head when his little sister coyly revealed the dildo and strap-on harness inside. There were so many things he wanted to ask and the most pressing one was, "H-how'd you get one of those?!" He didn't think even the shadiest sex shop owner in Spikemuth would let a girl Marnie's age inside, let alone make off with anything.

"Asked one of girls from Team Yell t'help me out." Piers blanched at the thought of one of the local Trainers going off to buy something like that for him. It wasn't exactly a secret in a town like this, but he preferred that other people think about the peculiarities of his sex life as little as possible. Marnie must have realized his horror, because she quickly tried to reassure him. "Don't worry, she thought I wanted t'use it with Gloria!"

The anxiety blessedly faded, and was supplanted by a different sense of unease. "Gloria?" Piers had his fair share of time with the girl, before and after her upheaval during the Champion Cup. He knew that she was rivals and friends with Marnie, and Piers was happy to see his little sister getting along with a girl her age. Were they fooling around on top of that?

Sure, he hadn't told Marnie that seeing other people was out of the question—hell, Piers expected her to find someone else sooner or later, someone who'd suit her better, that wasn't her own flesh and blood. But this, this was sooner than he'd ever wanted, and she hadn't even mentioned it before. Piers ventured as nonchalantly as he could while his head was buzzing with all sorts of thoughts, "Is she your..."

Before he could finish, he realized that Marnie was staring at him like he was an idiot and well, maybe that was deserved. "She just got this idea that me an' Gloria were a thing, so I figured I might go along with it. Worked out, didn't it?" Her brow furrowed and her voice was firm when she added, "And you _know_ I wouldn't do somethin' like that without tellin' you first."

Piers felt a twinge of shame for letting his insecurity get the better of him. "Sorry, Sis." He did feel lighter regardless, knowing that Marnie was still all his, and his shoulders relaxed. Though there was still the matter of what Marnie had bought for him. He stared down at it, finding he couldn't immediately complain about the red and black harness, or the look of the flesh-colored dildo. In fact, they both seemed pretty high-quality. How much did Marnie drop on it? Did she end up spending all her pocket money from the Gym Challenge?

"Ya don't have to if you don't wanna," Marnie offered. Years of being together on their own had made it easy for her to read it whenever he was having doubts, even when he thought he was hiding it well. "I thought... it might help."

Piers looked at the tool more closely. While not particularly large, it was a well-shaped, realistic-looking cock. Truthfully, he'd considered wearing something like it more than once, but more immediate was the fear that it would only remind him how much he was lacking. It was hard to put the feeling into words inside his own head, let alone try explaining it to Marnie.

"It's fine if you wanna try it out," he told her finally. If it was for his sis, Piers wouldn't mind taking the plunge once and for all.

He thought Marnie would be happy with his answer—she was always telling him he needed to stop second guessing himself over every little thing. Instead, her green eyes turned away from him and she touched the spot over her heart, the way she did when she was bothered. "It's not just that I wanna try it! I want ya to feel good too, big bro. You're always makin' me feel so amazing, but I can't ever return the favor." She raised her head slightly, like she was afraid that Piers would be upset with her for going out of her way. "You said ya didn't like gettin' touched straight on, so I thought it would be alright... Still no good?" Even if Piers had been ruffled by her sudden purchase, there was a bigger part of him humbled by how much thought Marnie put into doing something for him.

More importantly, however, Piers had to let her know that she didn't have to do anything in return. How hadn't he noticed it before, that Marnie was under the mistaken impression that he wasn't getting anything when they were together? "Sis," he said firmly, reaching out to cup her cheek. "I already feel really good whenever I make you come. I love eatin' you out. It gets me off like nothin' else." His voice dipped a little low, the taste of Marnie's cunt still lingering on his tongue. "So don't think you're not doing it for me, alright?" A faint blush painting her cheeks, Marnie nodded at his words. "I'm just worried it won't be any good for either of us. But... I am kinda curious about it," he admitted. "We might as well find out together before I write it off entirely, huh?"

Marnie's expression lightened, and she squeezed his hand. "I'd really like that. An' you know you can stop right away if it doesn't work proper! I love what we normally do together, too..." She was all too eager to reassure him that everything would be alright no matter what. At times like this, Piers was sure he didn't deserve the lovely young woman his little sis was shaping into.

"Got it. Next time, alright?" Piers gave a kiss to her hair. As much as Marnie seemed ready to launch right into it, he needed some extra preparation to feel secure about using a strap-on. Nothing would be less sexy than fumbling awkwardly with a harness for thirty minutes after getting Marnie all excited over it.

Next time turned out to be longer than either of them had anticipated, with Marnie still settling into her new position as Gym Leader and school getting back into full swing after the conclusion of the Gym Challenge. Piers was quietly grateful for the reprieve, though he knew his sister would be all too willing to give him the time he needed.

The harness had been uncomfortable on his hips at first. As he grew accustomed to fastening the straps, the sensation of it sitting against his pelvis wasn't quite as foreign. Sometimes, when he adjusted the dildo in his hand, a spark shot up his spine and it almost felt properly connected to him. Of course the dick Piers pictured in his head was a little bigger, but the dildo was well-suited for his baby sister. A part of him had been quietly terrified by the possibility that he might hurt Marnie with it because of the lack of physical feedback, so the smaller size was a relief. She was a petite girl, after all, and sometimes Piers had trouble getting three fingers inside her.

As fine as he'd been wearing it in private, however, having it on in front of Marnie was something else all together. All his wrought confidence dissipated in a steady stream, leaving squirming insecurity in its wake. "Looks pretty ridiculous, doesn't it?" he blurted out, imagining what Marnie must be seeing right now. Even if she'd gotten it for him, it couldn't be what she hoped for—seeing the way the harness framed his bony hips, the dildo crudely protruding outward from his crotch in mock-arousal.

Marnie crept across the bed to meet him at the edge, and there wasn't a speck of disappointment in her expression. Instead, her eyes were running down his body, interested, _excited_. "Actually, I think it's pretty sexy, Bro." She was looking up at him through her lashes as she spoke, the way she knew that got him going. Her lithe form was lovely as ever in her lacy black babydoll, the one she'd begged him to buy for her months ago, determined to have an adult form of sleeping wear. Piers swallowed hard, well aware that Marnie was probably humoring him, yet falling for anyway. One of her slender hands reached out, then settled on his thigh. "Can I touch it?"

"Yeah," he breathed, "'course."

Her hand reached upward, bypassing the harness entirely to curl around the dildo. Slowly, she began to stroke at it, pumping its length in a modest pace. Piers didn't know what he was expecting to feel, but the warmth spreading through his lower half startled him. His breath hitched and he jerked his hips, pushing further into his sister's palm. The reaction brought a flush of delight to Marnie's face right away. "Good?" she asked, eyes bright.

Piers nodded his head, resisting the impulse to hump against Marnie's hand for more stimulation. He'd underestimated just how aroused she could get him. The sheer material of her nightdress did nothing to hide her nipples, or the fact that she wasn't wearing any underwear beneath, and she looked so gorgeous that he had to touch her. Brushing his fingers over Marnie's shoulder and lower, down into the loose neck of her dress. She sighed as he squeezed at her small breast and teased the hard nub with his thumb.

"Piers," Marnie said, drawing his attention squarely back to her face. Within a split second, her pink lips were against the tip of the dildo and then, sliding over it. A sharp breath fell out of Piers's mouth at the sight that had haunted his dreams since he was old enough to know who he wanted—his little sister eagerly sucking his cock. Marnie kneaded at the base with her fingers as she sucked more of it into her mouth, then drew back. There was a thin sheen of saliva left over the length. Her eyes caught his as he gaped wordlessly. "You like it," she said with a victorious look.

He couldn't deny that, not when Marnie swirled her tongue over the tip in such an erotic way. "You really know how t'get me all—worked up." He was already throbbing from a couple minutes of Marnie's teasing, and with the way her thighs rubbed together under the hem of her skirt, he knew she had to be feeling it, too. Normally he would have taken the opportunity to give his little sister some relief, but he was reluctant to pull away so soon. And Marnie looked so delighted to have this effect on him--so he gave in to impulse. He gripped at her hair, not quite holding her head stable, but urging her to stay in place. She understood instantly and tilted her head up at him, deft tongue firmly pressed to the underside of the crown.

This time, Piers groaned aloud. Oh-so carefully, he inched forward, determined not to make his little sister gag on it. Her face flushed deeply, as hotly as Piers's whole body felt when he watched the tip of his cock disappear into Marnie's mouth, again and again. Marnie's hand dropped between her legs, stroking at her cunt in time with his movements.

Piers's earlier uncertainty was gone, replaced by pulsing desire, molten hot in the pit of his stomach. He caught his breath and slowly pulled his cock free from her lips. "Ya ready, Marnie? I... really wanna try it." He swallowed again, the idea of pressing into Marnie's little cunt so overwhelming that his mouth was practically watering.

Marnie was touching herself again, fingers moving in a teasing circle around her clit. "Fuckin' me, you mean?" The rough way she said it made his ears burn.

"Yeah." Piers brushed his hand along Marnie's delicate jawline, down to her chin, and thumbed her wet lips. "I want to fuck you, Sis." Her eyes darkened, and he could see the goose flesh breaking out over her shoulders.

Piers's heart was thumping as he watched her move into position across the bed for him. She stuffed a couple pillows underneath herself to prop her hips up, and Piers poured a generous helping of lube over his length. Marnie's legs were parted and waiting for him, her cunt glistening wet from arousal. He'd never thought he'd actually take his baby sister like this, content with using his fingers and tongue to make her go wild. Now that the opportunity was presented before him, Piers wanted nothing more than to thank Marnie for getting the ball rolling. And the best way to show his gratitude would be to give his sis the best time he could.

Settling on the bed in front of her, he gave her a quick reminder. "I won't be able t'feel it as much inside you, so you gotta let me know if it hurts, alright?"

Marnie wasn't worried at all. She shifted on the pillows and reached down to spread the swollen lips of her cunt open for him. "I practiced a lil, too," she said, lashes lowering with her voice. "I'll be able to handle ya just fine, big bro."

Piers didn't know where he wanted to look more when he finally sunk the tip inside her—Marnie's tight pink cunt swallowing it one centimeter at a time, or her face, eyelids fluttering closed and mouth parted as she let out a long gasp. He pushed inside her, hissing when he made it to the hilt. It was natural to move into the feeling of it, rocking against Marnie's body in shallow thrusts. "Yeah," she huffed, her legs curling around his thighs, "like that."

That was all the encouragement he needed to make good on his promise of fucking her. He started nice and slow, the way he always did. It was more awkward using his hips to do it compared to the finesse of his fingers, but he still knew what Marnie liked the most. How she liked a gentle build-up, long thrusts, then rougher until she was all but crying for more. Fuck, Piers could feel the way Marnie's cunt clenched around the thickness of his cock as he fullly pulled out, and couldn't avert his eyes when he plunged it back inside.

Rolling his hips against her, he slid his hands underneath the thin fabric of her babydoll and stroked the soft skin of her stomach and chest. Marnie was already starting to develop at her age, the swells of her breasts feeling fuller in his palms every time he had a proper moment to explore them.

"I can take it harder," Marnie told him, biting her bottom lip. Piers responded with just what she asked for, driving himself more firmly inside—adrenaline and excitement surging through him when Marnie clutched at his legs and moaned.

"You like that, Sis?"

"Y-yeah," she answered, voice pitching higher at the end of his thrust. Her eyes, hazy with pleasure, fixed on his. "You feel so good inside me." Piers didn't think he could get any more turned on before he heard that husky whisper. Craning his neck down, he caught Marnie's sweet lips with his own, coiling his tongue around hers as though he wanted to suck up every sound of pleasure and praise she gave him. Pinching at her breasts, he fucked her harder, loving the way Marnie reacted to him, the way she breathed into his mouth and dug her nails into his skin.

"Oh, Piers!" Marnie broke the kiss with a gasp, her body winding tight. "There!" Her legs squeezed around his legs and she bucked upward into him, desperately rubbing her swollen clit against his equipment. Every one of Marnie's movements sent shocks of pleasure running through his core, and the sight of Marnie fucking herself on him was so sexy he nearly couldn't contain himself. His arms folded around her, lifting her by the waist and grinding against her in return.

A soft sound not unlike a sob left Marnie's mouth—her perfect tell for when she was about to come hard—and her taut, sweat-soaked body went suddenly lax. Piers knew just what her twitching cunt was like on his fingers, could practically feel it now. He choked back a moan, still moving while he was deep inside her. "Ah!" Marnie trembled, overwhelmed, gripping hard at his hips.

"Sis," Piers gasped, half in apology and half pleading, still shamelessly rutting himself against her cunt. Waves of pleasure crashed over him as it all reached a peak—the feeling of Marnie's warm body, her wet cunt wrapped around him, her cute tense expression when she was being overstimulated, the little whimpers she made. Piers came with a guttural groan, holding Marnie tight to his chest. All he could think was how much he absolutely adored his baby sister, that no one else would ever be able to make him feel as whole or as wanted or content, even if he searched the entire world.

His senses came back to him gradually as his breathing evened out. Piers pulled gingerly out of her and unhooked the harness, mentally promising to give it a good clean as soon as he had a moment. For now, Marnie was already pulling him into position against her side, all but demanding he bask in the afterglow with her while it was still fresh.

She sighed in relief as Piers cradled her in his arms and pressed a kiss to her neck. "Sorry, Marn. Got pretty excited at the end there..." It was a bashful apology. Thankfully Marnie didn't seem cross with him, her expression filled more with curiosity than anything.

"Didya come?" she asked, quietly hopeful.

Her sincerity was enough to make him flustered as he nodded. "Yeah. You were great, Sis."

Marnie gave him a small smile and nuzzled his shoulder, all too happy to take the compliment. "You're forgiven then. Wanna... try it again sometime?"

Despite his initial misgivings, the strap-on had surpassed his expectations. While it didn't take much stimulation to put Piers over the edge after making Marnie come—the sight of her and her cute noises were always enough to make him lose his mind—he never thought he'd actually be able to orgasm in it. And he'd really enjoyed thrusting into her with a cock of his own. Not to mention how brilliantly Marnie had taken it and was even excited for more. How could he not want to do it again? Hell, maybe he'd be able to pick out a dick that was more to his liking one of these days...

For a moment, he went off in his own little world, thinking about his little sister's cunt squeezing down around a thicker shaft. Marnie was still watching him, and raised an eyebrow at his lengthy silence.

Piers cleared his throat. "I'm kinda sore after all that. Your big brother's not a spring chicken anymore, y'know..." Marnie recognized the slight deflection immediately for what it was, a smokescreen for his embarrassment about how much he'd liked it. Her lips spread in a devilish grin and she pulled him into a quick kiss.

"That so? Like they always say, practice makes perfect."


End file.
